The present invention relates to metal closures which are threadedly received on the neck of a container and have a pilfer-proof skirt. The invention also relates to apparatus for forming such a closure.
The use of threaded closures to replace the conventional crown has become more and more popular in recent years, particularly in the carbonated beverage industry. The primary advantage of a threaded metal bottle closure is that the bottle can be resealed after it has initially been opened.
One type of threaded closure that has been used includes what is known as a pilfer-proof skirt which initially is formed as an integral part of the closure and which is separated from the closure when the closure is initially removed from the bottle. This type of pilfer-proof skirt is formed by producing circumferentially spaced slits around the peripheral lower edge of the closure and the slits are separated by small bridges which are ruptured when the closure is removed from the bottle leaving the pilfer-proof skirt on the bottle. Because of the recent public interest in recycling of containers, such a closure has serious drawbacks since the pilfer-proof section cannot readily be removed from the bottle for recycling purposes.
In order to avoid such objectionable permanently retained section on the bottle, a more recent development in pilfer-proof closures is disclosed in U.S. Pat. No. 3,601,273 wherein the closure again has circumferentially spaced horizontally extending slits around the peripheral lower edge thereof with vertically extending score lines in the lower portion of the closure that defines the pilfer-proof or tamper-proof section of the closure. In the closure illustrated in this patent, the vertical scores are ruptured when the closure is initially removed from the bottle. Because the vertical scores are randomly positioned on the pilfer-proof sections, some scores may be in alignment with the horizontal slits which may produce sharp pointed sections that project outwardly when the closure is initially removed from the bottle and results in a hazardous condition for anyone attempting to reuse the closure. This type of closure is formed by initially stamping a cap from a flat sheet with a press and producing internal vertical scores extending from the free end of the caps. The cap is transferred to a rolling machine which includes a stationary mandrel with a plurality of spindles that are moved around a circumferential path around the perimeter of the mandrel and are simultaneously rotated about their own axes. The spindles support the metal caps which are simultaneously knurled and the peripheral circumferentially spaces slits are formed therein. The closures are then placed on a bottle in another rolling operation which forms the threads in the closure wall and simultaneously deforms the free edge of the closure inwardly below a bead that is on the neck of the bottle.
Quite recently a new type of pilfer-proof closure has been developed, which is disclosed in Hannon, U.S. Pat. No. 3,861,551 and is similar in many respects to the previous closure discussed above. The unique feature of the closure shown in the Hannon patent is that the vertical scores on the pilfer-proof skirt are accurately positioned with respect to the bridging members between the circumferentially spaced horizontal slits to prevent the formation of sharp pointed sections which project outwardly from the skirt.
The closure of the Hannon patent also incorporates apparatus for producing the closures disclosed therein and the apparatus and method for forming such a closure are covered by U.S. Pat. No. 3,824,941. The apparatus disclosed in this patent consists of initially forming an upper knurled band on the cap, subsequently forming a lower outwardly extending bulge which may also be knurled to produce a second band and subsequently slitting the outwardly directed bulge and scoring the skirt portion below the bulge.
The apparatus for producing the slits and scores is theoretically capable of producing the closures disclosed in U.S. Pat. No. 3,861,551. However, actual practice has shown that the apparatus is not economically feasible for being used as production equipment. It has been found that the particular cutting mechanism proposed for producing the horizontal circumferentially spaced slits produces a tearing action at opposite ends of the respective slits which may result in sharp edges being developed during the formation of the slits. Also, the multicomponent arrangement for producing the vertical score is practically impossible to manufacture on a commercial scale because of the extremely close tolerances that must be maintained in producing such apparatus. Furthermore, the multicomponent arrangement requires repeated realignment to maintain the required tolerances. It will be appreciated that a closure of this type has a wall thickness on the order of 0.010 inches and the vertical scores must be accurately controlled to produce an acceptable closure that consistently has scores of uniform depth.
Another problem has been observed in using the Hannon type closure. During the rolling operation which attaches the closure to the bottle, it has been observed that the vertical scores are at least partially severed adjacent the free edge and the severed edges are overlapped which tends to indicate that the closure has been removed at least once. While the obvious solution to such problem would be to increase the thickness of the residual for the score, such solution is not acceptable because it would increase the force or turning torque required for removing the closure.